1. FIELD OF THE INVENTION
My invention discloses new and useful improvements in antennae designs and comprehends usage in fixed station and mobile applications, in the VHF to microwave frequency regions.
It envisions a mechanism and a method for matching the impedance of a radiator to the impedance of a feedline and for isolating the radiator from the feedline.
The antennae are ground independent, capable of efficient performance without the need for any ground plane or ground simulating radial.
2. DESCRIPTION OF THE PRIOR ART
It has been known to use a non-resonant cavitylike construction overlapping a feed point for the purpose of impedance matching.
Berndt's patent #2,802,210 would appear to disclose such. In actuality, however, his cavity is not a choke. If it were, his lower element would be unable to function as described. He merely uses an extension of a choke surface for the tuning purpose. He doesn't use the open end of that choke for such purpose, nor does he use a dielectric in the tuning function.
Significantly, the cavity at his feedpoint is not resonant and does not form an open 1/4 wave transmission line at the operating frequency or any length close to a 1/4 wave at the operating frequency.
It is the impedance and not the resonance which he changes by a selective positioning of a short circuit slide 15.
Berndt's 1/4 wave choke or filter isolates currents from his feedline and is the only 1/4 wave device he uses.
Berndt's filter has an open circuit end facing away from his feedpoint and is not used for impedance matching or conversion from an unbalanced to a balanced feedline configuration.
The Berndt design relates to a center fed antenna relying on currents flowing down the outside of his conductive member.
Contrariwise, and as is about to appear in this disclosure, the antennae hereof are end fed, the cavities of which are sharply resonant chokes capable of preventing currents such as Berndt uses from flowing beyond their feedpoints and down the respective choke exteriors.
Equally deserving of citation is Hampton, #3,588,903, who provides no cavity function, his outer shell being short circuited by having its top and its bottom electrically connected to a coax shielding so as to allow a shorted secondary 1/4 wave coaxial section where the outer braid of his coax defines an inner conductor and the inner surface of his outer shell defines an outer conductor. This essentially is the well-known configuration which provides the balun action.
He provides an insulating material but in no way is it utilized as a tuning device or is it adjustable in any way and/or for any purpose
Patentee Hampton indicates that the tuning or matching function is accomplished by networks of series-parallel circuits 15.
Being fully aware of Ploussios, #4,509,056, I respect it only as a teaching of a choke system for defining the outward end of an antenna which in all cases are fed at a low impedance point, meaning an impedance value of approximately 70 ohms. Further he shows a center fed 1/2 wave dipole, known for its low impedance value. Contrariwise, my concept utilizes a high impedance feed point at the end of a 1/2 wave element and approximating 100,000 ohms.
Ploussios does not use his choke as a feed point impedance matching device. By an adjustment of his dielectric in the choke, he creates an infinite impedance but at the open end of the choke and not at the feedpoint. One end of his choke is shorted and the other open end is positioned away from his antenna feed point.
As will appear hereinafter, the choke of the present invention is shorted at one end and has an open end which faces toward the feedpoint so as to allow a feedpoint impedance transformation between the coaxial feed line (typically 50 ohms) and high impedance (approximately 100,000 ohms) at the end of a 1/2 wave element.